The present invention concerns a method for producing shaped articles having a high mechanical strength by applying a technique of electrodeposition on an aqueous suspension of a fibrous substance having an electrophoretic property, and an apparatus for producing the same.
The herein used term, "a fibrous substance having an electrophoretic property" means a fibrous protein such as collagen contained in skins and tendons of mammals, fibroin in silk, keratin in hair, fibrinogen in blood, myosin in muscles and casein in milk, as well as polysaccharides having a fiber-forming property such as chitin and alginic acid.
Hitherto, methods for producing shaped articles such as casings for packing of sausages, threads for surgical operation, guts for tennis-racket and sheets for artificial skin by electrodepositional shaping of a fibrous substance having an electrophoretic property, for instance, a proteinous fibril such as collagen have been known. The above-mentioned publicly known method, for instance as is disclosed in Japanese Patent Publication No. 13636/1971, comprises a process in which an aqueous suspension of the above-mentioned proteinous fibril is supplied into a vessel provided with at least one cathode and at least one anode, and by impressing a direct electric potential between the two electrodes, the above-mentioned proteinous fibril is accumulated electrodepositionally onto the surface of one of the electrodes to form shaped articles.
In the above-mentioned method, when the pH of the above-mentioned aqueous suspension is adjusted to lower than 6, the proteinous fibrils are electrically deposited selectively on the surface of cathode, and on the other hand when it is adjusted to higher than 9, the proteinous fibrils are electrically deposited selectively onto the surface of the anode.
However, in the above-mentioned method of electrodeposition, when the operation is continuously carried out, since the electrodeposited shaped articles are continuously removed away from the electrode and the aqueous suspension of the proteinous fibril is continuously supplied into the vessel of electrodeposition as a raw material, the proteinous fibrils in the aqueous suspension electrophoretically move to the almost same direction as the direction of the flow of the aqueous suspension (the aqueous suspension flows to a fixed direction in the vessel of electrodeposition) and deposit on the surface of electrode.
Accordingly, the electrodepositionally shaped articles have a structure in which the proteinous fibrils are oriented almost into one and same fixed direction and so, there is a defect that the article is mechanically weaker.
In consideration of the above-mentioned situation, Japanese Patent Publication No. 24257/1972 proposes the following method according to which the mechanical strength of the shaped articles obtained by the process of continuous electrodeposition will be improved.
That is, in the case where an aqueous suspension of proteinous fibril of protein is continuously introduced into the vessel of electrodeposition in the same procedures as described above and the proteinous fibrils are electrically deposited from the suspension to the prescribed surface of the electrode, and the thus shaped articles by electrodeposition of the proteinous fibril is continuously removed from the vessel, the aqueous suspension in the vessel of electrodeposition is given a flow to the direction different from the direction of removing the shaped product and thus the fibrils being deposition in the shaped article take an entangled structure and the mechanical strength of the shaped article is improved.
In addition, the apparatus for production of the above-mentioned shaped articles disclosed in the above-mentioned Publication comprises a vessel for electrodeposition provided with at least one pillar-shaped electrode for the base of electrodeposition, at least one opposing electrode, a means for continuously removing the pipe-shaped articles electrically deposited on the surface of the above-mentioned electrode for the base of electrodeposition from the vessel for electrodeposition and a means for giving a flow of a different direction from the direction of removing the above-mentioned formulated objects to the aqueous suspension of proteinous fibrils, introduced into the vessel for electrodeposition. The means for giving the above-mentioned flow to the above-mentioned aqueous suspension disclosed in the above-mentioned Publication comprises a method in which a spirally ascending flow is caused in the above-mentioned aqueous suspension by installing spiral ribbon(s) in the inner surface of the vessel for electrodeposition and by forwarding the aqueous suspension from the lower region of the vessel to the tangential direction against the cross section of the vessel, or a method in which a rotary flow is caused in the above-mentioned aqueous suspension by rotating a stirrer around the above-mentioned pillar-shaped electrode onto which the fibrous substance is to be electrodeposited, the stirrer having been installed on the opposite electrode or installed separately.
However, according to the method and the apparatus disclosed in the above-mentioned Japanese Patent Publication No. 24257/1972, although the proteinous fibrils in the shaped articles obtained as the articles electrodeposited onto the electrode have entangled mutually owing to the intra-vessel flow of the aqueous suspension into the different direction to the direction of removing the shaped articles, since the above-mentioned aqueous suspension has only one direction of rotation, the shaped article obtained as the electrodeposited body on the electrode is composed of a single layer in which only one and same structure substantially presents. Accordingly, the mechanical strength of the shaped article obtained by the application of the above-mentioned method and apparatus is not satisfactory.
The inventors of the present invention, as a result of studies based on the presumption that the mechanical strength of the electrodeposited shaped article consisting of the above-mentioned fibrous substance will be remarkably improved by giving the shaped article a laminated layer structure of the fibrous substance, each layer having direction of orientation of the fibrous substance different from each other, have found that in the process of electrodeposition, such laminated layers in the deposited shaped articles are available and as a result, the mechanical strength of the thus obtained shaped article is extremely improved by causing at least two flows different from each other in direction in the aqueous suspension of the above-mentioned fibrous substance during the operation of electrodeposition.
Accordingly, one object of the present invention is to offer a method for producing, from an aqueous suspension of an electrophoretic fibrous substance, the shaped articles excellent in mechanical strength comprising a structure of laminated layers of the fibrous substance, in which the direction of orientation of the fibrous substance in the layer is different from layer after layer.
Another object of the present invention is to offer an apparatus for producing continuously the above-mentioned shaped articles from the above-mentioned aqueous suspension of the fibrous substance.
Still another object of the present invention is to offer shaped articles having a high mechanical strength comprising laminated layers of the above-mentioned fibrous substance, the direction of the orientation of the fibrous substance in each layer of the laminated layers being different from layer after layer.